The rivalry between the fashion houses of Christian Dior and Yves Saint Laurent, who each presented collections by new designers, has spilled into the open and ended Paris fashion week with an ugly slanging match.

With tempers running high and long-held grudges made public, Hedi Slimane of YSL now finds himself waging a public war, not against Raf Simons of Christian Dior but against the fashion editor of the New York Times.

Dior played their hand first in a contest that seemed initially both evenly poised and tempered. The show garnered rave reviews. Writing in the International Herald Tribune, the revered fashion editor Suzy Menkes said "it was the roar that went up backstage behind the wafting pastel curtains, echoing the clapping in the graceful interlocking salons, that proved the designer Raf Simons had exceeded all expectations". Vogue called it "a resounding success". The influential catwalk website style.com dubbed it "a special kind of twenty-first century glamour".

But a faint mood of fractiousness has emanated from the house of Yves Saint Laurent since June, when Hedi Slimane dropped the 'Yves' from some aspects of branding, giving clothes of his design (but not other items such as perfume, or keyrings) the label Saint Laurent or Saint Laurent Paris. At that time the house reacted angrily when the press, focusing on the thrust of the story rather than the detail, suggested that the move represented a break with the past. Slimane's spokespeople were at pains to explain the move was intended to forge a direct connection with the Saint Laurent Rive Gauche label set up by Yves himself in 1966.

The height of the bar set by Christian Dior's show did nothing to lighten the mood at YSL. In the run-up to Monday's show journalists were issued with unusually strict instructions as to what behaviour would be tolerated backstage. Photographs and questions, both of which are a standard part of the informal debrief session that takes place after a show, were banned.

YSL did not fare as well with the critics as Dior. The floppy hats, sheer capes and frilled blouses were too close to the YSL archives to please an industry on a perennial hunt for the new. "Witchy seduction was the agenda of the evening. A bizarre way to stake a claim to one of fashion's most unimpeachable legacies," was the verdict from style.com. Womenswear Daily described the collection as "costumey". (I felt it was "unmodified nostalgia" and "lacking in relevance to the real world".)

The most hard-hitting review came from Cathy Horyn, the longstanding fashion editor of the New York Times, who had not been invited to the show. Her review, which described the clothes as "nice but frozen", called attention to "the self-important air of Saint Laurent's media relations" and claimed her ban was part of a grudge held against her for an article eight years ago in which she wrote that the game-changing skinny silhouette attributed to Slimane – a look which made him a fashion demigod during a stint designing YSL menswear – was conceived not by Slimane, but by Raf Simons.

It was the latest thrust in a catwalk season that had been punchy even by the feisty standards of Horyn, a globally respected critic whose tongue can be harsh. Last month, after Horyn wrote that Oscar de la Renta was "more of a hot dog than an éminence grise of American fashion", de la Renta took out a full-page ad in Womenswear Daily comparing Horyn to "a three-day old hamburger".

Less than 12 hours after Horyn's review was published Hedi Slimane tweeted a riposte, describing Horyn as "a schoolyard bully", and mocked her good relations with Christian Dior, dubbing her "a publicist in disguise". When Horyn declined to comment on the row, describing it as "silly nonsense", Slimane took to Twitter again, calling her "an embarrassment for the newspaper". YSL declined to comment, demurring that Slimane's Twitter page was a personal matter.

The row has shone a harsh and unflattering light on the fashion industry. What had seemed a gentlemanly rivalry between two designers whose design synergy lent them a common purpose in modernising the Paris fashion world is recast as a long-running grudge match. It also gives rare insight into the delicacy of personal relationships in an industry where personal chemistry, critical opinion and commercial considerations can come into conflict.

The shakedown from a tumultuous week in Paris has been complicated further by reports that retailers took a far more positive view of the Saint Laurent show than critics. While reviews are read straight away, the views of buyers often take several days to filter into public view. A report in Womenswear Daily quoted many important buyers warmly praising the collection.

Mark Lee of influential New York store Barneys described "a unanimous and spontaneous love from all the Barneys team members immediately following the show", while Marigay McKee of Harrods pronounced it "perfect for our customer". The feeling among many retailers is that this rendering of a recognisable YSL look will make for a profitable season.

If the buyers' predictions are true then YSL, having looked to be on the ropes, may yet have the last laugh.